Tantalum target for Metallica + MSDS

Sebastian J. Osterfeld sjo at stanford.edu
Mon Dec 13 14:59:01 PST 2004


I would like to purchase and use a Tantalum target to passivate my wafer 
in Metallica and to provide an adhesion layer for gold at the same time. 
I know I could use Cr, Ni, or Ti as well, but everyone in my group 
insists Tantalum that is the best and most common thin surface 
passivation. Here are the details:


1. Requestor name:
Sebastian J. Osterfeld

2. Phone number:
650-906-1946

3. email address:
sjo at stanford.edu

4. Requestor’s PI (Advisor) or Company:
Shan X. Wang, Materials Science / EE

5. The name of the new Chemical (give all names commonly used):
Tantalum (Ta)

6. If there are secondary new chemicals that must be used with this 
material, such as a developer for a new resist, list each of them here 
and supply MSDSs for each of them.

7. Name of vendor/manufacturer that you are planning to obtain this 
material from:
Kurt J. Lesker Company

8. URL for vendor’s website where info on the proposed chemical can be 
found:
http://www.lesker.com/newweb/Deposition/Sputter_Targets/ElementNames_T/Tan_Tantalum.cfm?CFID=230181&CFTOKEN=41620656&section=tantcomps&init=skip

9. Vendor’s address and phone number:
Kurt J. Lesker Company
PO Box 400084-W
Pittsburgh, Pa 15268-0084
(412) 233-4200 or (800) 245-1656

10. What is your reason for wanting to bring this material into the lab:
To passivate wafers and provide adhesion to a gold sputtering layer. Ta 
is actually a common last layer on spin valves and other sensors.

11. Make a strong case why you can not use an already approved 
chemical/material for this purpose:
Ti and Ni are more reactive than Ta. The substrate I am using is also 
going to be used for spin valve fabrication, and as such, Cr is 
undesirable due to the magnetic properties of its oxide. Moreover, spin 
valves are most typically capped with Tantalum, which can form a very 
high quality passivation layer. Consider, for example, that some of the 
smallest electrolytic capacitors are Tantalum capacitors: This is 
exactly because Tantalum oxide is if such high quality even on 
comparatively thin layers.

12. (Note that all previously approved chemicals are listed in the MSDS 
Index binder located in the receiving area. Also see SNF Index of MSDS 
Sheets.)
Yes, I do know that the receiving area has the MSDS sheets. I don't see 
Ta in the online MSDS index, and I will check out the paper MSDS sheets 
just to be sure.

13. List all the lab equipment and wet benches that you propose to use 
with this chemical:
- Metallica for deposition
- wbsolvent (for lift-off)

Subsequent processing:
- svgcoat
- svgdev
- evalign
- YES oven
- More liftoff

14. Proposed quantity of the chemical that you want to bring into lab 
(give both raw and mixed quantities):
One 1" disk, ca. 20g or less

15. State the form that the proposed chemical is in. (Is it solid, 
powder or liquid? Note: as a general rule, powders are not permitted in 
the cleanroom.):
Solid metallic disk

16. State whether the chemical needed to be mixed to use it:
None, occasional cleaning with IPA.

17. From manufacturer, vendor or the Stanford safety site, obtain a 
legible Material Safety Data Sheet (MSDS) for all the proposed 
chemicals. Send these to the person listed below.
Tantalum and its oxide are of generally low toxicity. Attached you will 
find two MSDS sheets.

18. If the chemical/material is to be used in any the "clean" equipment, 
purity specifications will be needed. This is most important for 
chemicals/material that are not normally used for VLSI device 
fabrication. To be allowed into a "clean" tool, the material should MOS 
grade or better.
I do not intend to use it on any clean equipment.

19. Read the MSDSs as well as the Stanford Chemical Storage Groups and 
the Stanford Chemical Safety Data Base sections on this website to 
determine the Storage Group Identifier and Main Hazard Class of your 
chemical/material.
Storage group: G Non-Reactive Materials and Non-Hazardous Materials.
Main Hazard Class: 11. Non Hazardous

20. Determine whether there is enough room to store your material in the 
designed lab storage areas. Storage groups A,B,D and L are stored in the 
yellow solvent cabinet in the furnace support area, while storage groups 
C, E, F and G are stored on top of one of the Pass-through Carts. Ensure 
your chemical container or material is properly labeled. If there is no 
available room, it must be stored by in the bulk storage area. You will 
then need to obtain it from receiving area personnel each time you want 
to use it and return it to them when you are finished using it (or each 
time you leave the lab). Note that there is no storage of 
chemicals/materials in the processing lab or at any wet bench.
Yes, there is enough storage. I would either take it home to my lab 
after work at the SNF, or keep it in the Metallica supply box with the 
other targets, thus making it available for general use.

21. In your discussions with vendors, try to determine the best way to 
dispose of your spent chemicals and by-products. The lab has acid/base, 
HF and solvent drains. The acid/base drains go to a neutralization 
system before going the city waste water system. The city of Palo Alto 
has tight limits on the amount of heavy metals that be disposed of 
through the waste water system. If your chemical contains any metals, 
there is a good chance that you will have to collect all your waste and 
dispose of it in labeled containers which are picked up the Health and 
Safety Department. The HF drains go to a central tank which is pumped 
out by a HF disposal service at considerable expense on a regular basis. 
The solvent drains in the solvent benches are collected under the 
benches and disposed of by Heath and Safety as needed.
The excess Ta that would be lifted off will enter the solvent canister. 
The solid target, when finally used up, can be brought to regular 
consumer metal recycling places due to its low toxicity.

22. Put together a detailed process flow description on how you proposed 
to use this chemical. This should include: Any chemical mixing, all lab 
equipment and wet benched to be used, all containers to be used, where 
chemical is to be stored and how chemical and by-products are to be 
deposed of. This should be in a Word file attached to your e-mail 
request. In reviewing your procedure, we will be most interested in how 
the safety and contamination issues are to be dealt with.

Due to the simplicity of application, I will omit the word file in favor 
of an immediate description:

- Mixing: Ta will be sputtered in conjunction with gold in Metallica. 
Contamination is not to be expected, but targets can be pre-sputtered 
for cleaning.
- Equipment: Metallica, WBsolvent, SVGDev, SVGcoat, EVAlign, Headway
- Containers: WBSolvent glassware, SVGDev casettes, YES oven casettes, 
Wafer storage boxes
- Storage: Metallica target storage box
- Disposal: Minimal waste is created as a result of lift-off processing. 
The excess metal flakes would go into the solvent carboy.
- Contamination: Is not to be expected. Ta has low diffusivity, 
negligible vapor pressure at all encountered processing steps, and is 
self-passivating.


-- 
Sebastian J. Osterfeld
PhD. Student / Shan X. Wang Group
Dept. of Materials Science & Engineering

Residential Mailing Address:
334 Olmsted Rd Apt 114
Stanford, CA 94305

Office Mailing Address:
McCullough Building, Room 208A
476 Lomita Mall
Stanford, CA 94305-4045

Home:	(650) 331-1171 (voicemail) 
Cell:	(650) 906-1946
Work:	(650) 723-2939
Fax:	(650) 736-1984 (at work)

Email: Osterfeld at stanford.edu 

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